Process for the hydrogenation of coal

ABSTRACT

A process for the hydrogenation of coal to produce a methanecontaining gas is described. Powdered raw coal is introduced into a recycling fluidized bed of noncaking material. The coal is rapidly heated and at least partly hydrogenated, and converted into a noncaking powdered char. The process is generally operated at temperatures of 600* to 1,000* C. and pressures of 10 to 200 atmospheres.

United States Patent Inventors Frederick James Dent;

Appl. No. Filed Patented Assignee PROCESS FOR THE HYDROGENATION 0F COAL9 Claims, 1 Drawing Fig.

us. Cl 48/210,

252/373 Int. Cl. C10j 3/00 Field of Search 48/214,

Primary Examiner-Morris O. Wolk Assistant Examiner-R. E. SerwinAttorney-Watson, Cole, Grindle & Watson ABSTRACT: A process for thehydrogenation of coal to produce a methane-containing gas is described.Powdered raw coal is introduced into a recycling fluidized bed ofnoncaking material. The coal is rapidly heated and at least partlyhydrogenated, and converted into a noncaking powdered char. The processis generally operated at temperatures of 600 to l,000 C. and pressuresof 10 to 200 atmospheres.

PROCESS FOR THE HYDROGENATION OF COAL This invention relates to aprocess for the hydrogenation of coal to provide a methane-containinggas.

The hydrogenation of coal to produce mainly gaseous h; drocarbonsnecessitates heating raw coal from cold to temperatures above at least600 C., the coal being conveniently in the presence of hydrogen underelevated pressure while it is being heated. lt is known that whenbituminous coals are heated through a temperature range near and aboveabout 400 C. their decomposition may be accompanied by partial fusionwhich can cause the pieces or particles of the coal to agglomerate orcake. The extent to which this occurs varies widely over a wide range ofcoal ranks, and in some circumstances it is possible to describe certaincoals as noncaking. However, the treatment of coal with hydrogen underpressure while its temperature is being raised through the caking rangeincreases the caking tendency and it is likely that there is nobituminous coal which is initially noncaking under the conditions used.lf fluidized bed techniques are to be used in the hydrogenation process,care must be taken to operate so that the caking properties of the coalthat are displayed as the coal is being heated do not lead tointerference with the working of the process. Once the coal has beenheated through the critical temperature range in such a way that itscaking properties have been destroyed, difficulty with agglomeration isavoided for operation at any temperature. w

We have found that it is possible to operate so as to avoid difficultyarising from the caking properties of the coal, and meanwhile to destroythese caking properties, by dispersing the coal into a hot recycling bedof fluidized noncaking material in the presence of hydrogen underpressure. The rapid heating experienced by the particles causes therapid hydrogenation of at least their more reactive constituents andthese are converted into a no-caking semicoke or char. At the same timethe dispersion of the particles in the bed prevents any transistorycaking tendency from causing buildup of ag' glomerates.

The invention provides a process for the hydrogenation of coal toprovide a methane-containing gas, which process comprises introducingpowdered raw coal into a recycling fluidized bed of noncaking materialat a temperature of from 600 C. to 1,000 C. and in the presence of anhydrogenating gas, the rate of introduction of the coal into the bed andthe temperature of the fluidized bed being such that the coal is rapidlyheated and at least partly hydrogenated and converted to a noncakingcondition.

The process may be carried out at pressures of, for example, from to 200atmospheres, preferably to 100 atmospheres, with hydrogenating gas atreaction temperatures of from 600 C. to l,000 C., preferably 700 C. to900 C. The hydrogenation results in the production of gaseoushydrocarbons (arising mainly, and especially at the lower temperatures,from the hydrogenation of the volatile constituents of the coal) and ofa residue of noncaking powdered char. This latter material may behydrogenated under severer conditions in a later state of the overallprocess to produce more methane and a residue which may be used forhydrogen manufacture. Alternatively, but less advantageously, all themethane required from the overall process may be produced in the onehydrogenation stage and the solid residue from it may be used directlyfor hydrogen manufacture.

The use of a fluidized bed facilitates the temperature control of thereactions, which are exothermic. The level of temperature is controlledby adjustment of the preheat temperature of the reactants, includingthat of the raw coal particles, but as there is a limit to thetemperature to which coal can be preheated, it may be necessary toprovide heat from other sources. Preferably, this is done by carryingout other exothermic reactions in the fluidized bed along with thehydrogenation reaction, for example, an oxygen-containing gas can beintroduced, or a light petroleum distillate can be fed and hydrogenated.

Preferably, the noncaking material constituting the fluidized bed is thenoncaking char produced by the hydrogenation of the powdered raw coalwhich is fed in. Material is extracted from the bed as and whennecessary. Preferably, the introduction of the coal and the extractionof treated char are both operated continuously. In starting up theprocess, the fluidized bed has to be initially noncaking and cansuitably be high temperature coke; as the treatment proceeds this isprogressively extracted and replaced by hydrogenated, noncaking charformed by the reaction. A stage is soon reached when the burden consistssubstantially completely of treated coal and the material extracted isof uniform composition suitable for the next stage of the completeprocess.

Suitable apparatus for carrying out the process of the invention is amodified version of the fluidized bed apparatus used for thehydrogenation of oil. The principal modifications required are thereplacement of the oil atomizers by nozzles or injectors through whichpowdered coal, entrained in gas (which may be hydrogenating gas) is fedinto the apparatus, and the provision of an offtake, by means of whichthe treated coal can be withdrawn by known means either continuously orintermittently.

Apparatus which can be modified for the present purpose is described inBritish Pat. Nos. 830,960 and 873,832, but it is preferred to use inpracticing this invention modified apparatus which is described in ourcopending US. Pat. application Ser. No. 566,947 US. Pat. No. 3,484,219,dated Dec. 16, 1969.

This latter-mentioned specification describes apparatus for performing achemical reaction between a reactant gas and fluid material to produce agaseous product, which apparatus comprises an elongated thermallyinsulated reaction vessel, to be held in a vertical position and tocontain a fluidized bed, having mounted within it at least one dividingmember which is shorter than the internal length of the vessel and whichdivides the interior of the vessel into at least two regions, at leastone 'to act as a riser for the fluidized bed and a region surroundingthe riser or risers to act as a downcomer therefor, all the regionsbeing in communication with each other beyond the ends of the dividingmember or members, means for supplying the reactant gas at the lower endof the reaction vessel so as to maintain at least one zone of ascendingparticles in the fluidized state in the riser or risers and a zone ofdescending particles in the fluidized state in the downcomer, at leastone nozzle associated with each riser within the reaction vessel forinjecting or atomizing the fluid material into the reactant gas and anoutlet for a gaseous reaction product at the upper end of the reactionvessel. When this apparatus is used, an additional outlet or offtake(for solids) can be provided from the base of the downcomer.

The invention will now be described by way of example with reference tothe accompanying drawing, which shows in diagrammatic form a sectionalside elevation of a reaction vessel in which the process of theinvention may suitably be carried out.

Within a pressure vessel 1 and separated from it by insulation 2 thereis a cylindrical reaction vessel 3 within which is a coaxial cylinder 4mounted so as to be spaced away from a shorter cylinder 5 by a gap 6.There is a shallow compartment at the base of the vessel which isdivided by the shorter cylinder 5 into a central cylindrical chamber 7'and an annular chamber 8. These chambers, which are constructedaccording to British Pat. No. 1,036,890, provide means for obtaininguniformity of distribution of the reactants into the cylindrical andannular spaces above the top surface of the compartment, which is aperforated plate 15. The insulating space 2 between the reaction vesseland pressure shell may be, but is not shown as, as in British Pat. No.1,044,007. Baffles 9 may be located above the end of the cylinder 4.

Pipe' 10 is for the introduction of the large proportion of thehydrogenating gas into chamber 7-and thence into the base of the centraltube 4. Pipe 11 is for the introduction of a further quantity ofhydrogenating gas into chamber 8 and thence into the annulus betweenvessel 3 and cylinder 4 to ensure proper fluidization, when theapparatus is in operation, of descending solid particles. Pipe 12 is forthe introduction of powdered coal, entrained in gas, the suspensionentering the reaction vessel at the open end 13 of pipe 12. Pipe 14 isfor the withdrawal of char.

The apparatus is charged with noncaking fluidizable solid, convenientlyhigh temperature or medium temperature coke, and circulatingfluidization (the solids circulate up cylinder 4 and down the annulusbetween cylinder 4 and vessel 3) is established by known means while thebed is being heated, say to 800 C., by known means which may includepreheating the hydrogen introduced through the distributors (pipes and11) in the base and by introducing air. A suitable method forestablishing the fluidized bed is described in our aforementioned U.S.Pat. No. 3,484,210. Meanwhile the pressure is being raised to say, 70atmospheres. When the chosen operating temperature has been reached, thesupply of powdered raw coal is started (through pipe 12), slowly atfirst, and is built up to a rate conveniently below that, ascertained byexperience, at which agglomeration is first encountered. It may then bepossible to stop or reduce the supply of air. The coal is rapidly heatedand converted to a noncaking condition. The withdrawal of solids isbegun at a corresponding rate so as to maintain the volume of the burdensubstantially constant. Temperatures are adjusted by control of thepreheat temperature of the input materials and pressures by the rates ofsupply and withdrawal of gaseous reactants and products. As indicatedhereinbefore, certain exothermic reactions may be conducted within thereactor if the heat liberated by the hydrogenation of the coal togetherwith that supplied as preheat is insufficient to maintain thetemperature. The powder withdrawn in the early stages consistspredominantly of coke and is rejected, but as withdrawal proceeds thematerial contains an increasing proportion of the residue from coal thathas been treated according to the invention. Eventually rejection of thesolid product ceases and its retention for use in later stages of theoverall process begins.

The following is an example of the process of the invention as carriedout in the above-described apparatus.

Example A weakly caking British (Nottinghamshire Arkwright) coal wastreated by hydrogenation under pressure, using as the hydrogenating gasa gas that was made by the gasification and hydrogenation of charresulting from the present process. The hydrogenation of the charproduces a gas of higher calorific value than that of the gas used tohydrogenate the char and further char from which more hydrogenating gascan be made.

In the apparatus the reaction vessel had an internal diameter of 16inches and the inner coaxial cylinder had an internal diameter of l 1inch and was 18 feet long. A charge of powdered char, formed by thereplacement of an initial charge of coke by the product of hydrogenationof raw coal, was kept in circulation up the central tube and down theannulus by the supply of the fluidizing hydrogenating gas at the base.The average linear velocity of solids flow up the central tube was 1foot per second. The temperature of the circulating bed was 800 C. andthe operating pressure 1,000 p.s.i.g.

The hydrogenating gas had the volumetric percentage composition s.c.f.per hour.

2,000 pounds per hour of the raw coal, of composition percent by weight)Mineral C H O S N H2O matter percent by volume. Its calorific value was606 B.t.u./s.c.f., that ofthe initial hydrogenating gas being 500B.t.u./s.c.f.

There was withdrawn from the reaction vessel 1,167 lb./hr. ofhydrogenated, noncaking char, of composition Mineral matter percent byweight. 35.7 lb./hr. of tar were also produced by condensation from thecooled product gas.

We claim:

1. A process for the hydrogenation of coal to provide amethane-containing gas, which process comprises introducing powdered rawcoal into a recycling fluidized bed of noncaking material at atemperature of from 600 C. to l,000 C. and at a pressure of from 10 to200 atmospheres in the presence of an hydrogenating gas, the rate ofintroduction of the coal into the bed and the temperature of thefluidized bed being such that the coal is rapidly heated and at leastpartly hydrogenated and converted to a noncaking condition.

2. A process as claimed in claim 1 wherein the process is carried out ata pressure of from 25 to atmospheres.

3. A process as claimed in claim 1 wherein the process is carried out ata reaction temperature of from 700 to 900 C.

4. A process as claimed in claim 1 wherein additional heat is suppliedto the fluidized bed by carrying out another exothermic reaction in thebed.

5. A process as claimed in claim 4 wherein the other exothermic reactionis established in the fluidized bed by introducing into the bed amaterial selected from the group comprising an oxygen-containing gas anda light petroleum distillate.

6. A process as claimed in claim 1 wherein the powdered raw coal iscontinuously fed to the fluidized bed, and the treated noncakingmaterial produced from the powdered material continuously withdrawn fromit.

7. A process as claimed in claim 1 wherein the process is operated suchthat the powdered raw coal is only partially hydrogenated, thehydrogenation being subsequently completed in a separate stage.

8. A process as claimed in claim 1 wherein the powdered raw coal isintroduced into the fluidized bed entrained in hydrogenating gas.

9. A process as claimed in claim 1 wherein the powdered raw coal ispreheated prior to being introduced into the fluidized bed.

2. A process as claimed in claim 1 wherein the process is carried out ata pressure of from 25 to 100 atmospheres.
 3. A process as claimed inclaim 1 wherein the process is carried out at a reaction temperature offrom 700* to 900* C.
 4. A process as claimed in claim 1 whereinadditional heat is supplied to the fluidized bed by carrying out anotherexothermic reaction in the bed.
 5. A process as claimed in claim 4wherein the other exothermic reaction is established in the fluidizedbed by introducing into the bed a material selected from the groupcomprising an oxygen-containing gas and a light petroleum distillate. 6.A process as claimed in claim 1 wherein the powdered raw coal iscontinuously fed to the fluidized bed, and the treated noncakingmaterial produced from the powdered material continuously withdrawn fromit.
 7. A process as claimed in claim 1 wherein the process is operatedsuch that the powdered raw coaL is only partially hydrogenated, thehydrogenation being subsequently completed in a separate stage.
 8. Aprocess as claimed in claim 1 wherein the powdered raw coal isintroduced into the fluidized bed entrained in hydrogenating gas.
 9. Aprocess as claimed in claim 1 wherein the powdered raw coal is preheatedprior to being introduced into the fluidized bed.